Bug: Missing changes from merge for version control settings

[js3110]

Description

After merging #1103 and #1059, some changes from #1103 were lost during the merge of #1059 into main. The merge conflict resolution in inst/shiny/modules/tab_nca/zip.R dropped the settings comment UI that #1103 added to the export modal.

Root cause

PR #1059 heavily restructured the export modal in zip.R (added slide customisation, validation, multi-step flow). When it was merged after #1103, the conflict resolution dropped the settings comment UI elements that #1103 had added.

What's missing in zip.R

Two pieces from #1103 were lost in the export modal:

1. Settings comment UI element (container + textInput)

The settings_comment_container div with the textInput should appear in the export modal (inside .show_export_modal()) after the "Data tables" format selector, hidden by default and shown when settings_file is selected in the tree. On the #1103 branch this was:

shinyjs::hidden(
  div(
    id = ns("settings_comment_container"),
    tags$br(),
    h4("Comment ", tags$small("(optional)")),
    textInput(
      ns("settings_comment"),
      label = NULL,
      placeholder = "e.g. final NCA, first draft"
    )
  )
)

The observer that shows/hides this container is still present (lines 435-442 on main) but is orphaned — it references a UI element that no longer exists.

2. Settings comment storage in ZIP download handler

The line that stores the comment value for use by .export_settings() is missing from the ZIP download handler:

session$userData$settings_save_comment <- input$settings_comment

Without this, zip-utils.R::.export_settings() always gets an empty comment (session$userData$settings_save_comment is never set during ZIP export), so versioned settings in the ZIP always have a blank comment.

To reproduce

1. Upload data, run NCA
2. Open the export modal (Save button)
3. Select settings_file in the export tree
4. No comment field appears (it should)
5. Export ZIP — the settings.yaml inside has an empty comment field

Expected behaviour

1. When settings_file is selected in the export tree, a "Comment (optional)" text input appears
2. The comment entered is stored in session$userData$settings_save_comment before ZIP creation
3. The comment appears in the versioned settings.yaml inside the exported ZIP

Fix scope

• Add the settings_comment_container div with textInput back into .show_export_modal() in zip.R, after the "Data tables" format selector
• Add session$userData$settings_save_comment <- input$settings_comment to the ZIP download handler (in the confirm_export or download_zip_configured observer, before the export runs)